Feasibility of Qualitative Evaluation and Quantitative T2 Mapping of Peripheral Nerves and Muscles Using GRAPPATINI.

Background: Quantitative T2 mapping holds promise for evaluating peripheral nerve and muscle disorders, but current methods lack speed and diagnostic feasibility. As a proof of concept, T2 mapping may be applied to assess the abnormality of the common peroneal nerve (CPN), leading to denervation of the tibialis anterior muscle and subsequent foot drop.

Purpose: To evaluate the GRAPPATINI sequence (a combination of generalized autocalibrating partially parallel acquisition [GRAPPA] and model-based accelerated relaxometry by iterative non-linear inversion [MARTINI]) for qualitative assessment and quantitative T2 mapping in patients with foot drop. We hypothesized that GRAPPATINI would yield comparable qualitative image quality to conventional T2-weighted (T2w) turbo spin echo (TSE) while detecting T2 differences between abnormal and normal nerves and muscles.

Study type: Prospective, cross-sectional study.

Population: 27 subjects (13 females; mean age: 54.4 years; range: 17-85 years) with clinical suspicion or diagnosis of foot drop.

Field strength/sequence: 3-Tesla, with GRAPPATINI T2 mapping (spin echo) and T2w-TSE Dixon for unilateral MRI of the knee region.

Assessment: Three radiologists, blinded to the sequence type and clinical data, evaluated nerve and muscle visualization, diagnostic confidence, and abnormal signal detection. Quantitative T2 values were measured in six manually segmented muscles and in the CPN and tibial nerve.

Statistical tests: Wilcoxon rank sum tests compared T2 values between abnormal and normal muscles/nerves (p < 0.05 indicates statistical significance). Intra-class correlation coefficients (ICCs) assessed interobserver agreement.

Results: Qualitative scores for nerve visualization, muscle visualization, and diagnostic confidence were similar between GRAPPATINI and T2w-Dixon (p = 1.0). T2 values were significantly higher in all abnormal versus normal muscles (66.5 vs. 45.7 ms) and in all abnormal versus normal nerves (66.8 vs. 60.5 ms).

Data conclusion: GRAPPATINI provided comparable qualitative image quality to T2w imaging while enabling quantitative T2 mapping to detect abnormalities in muscles and nerves in patients with foot drop.

Evidence level: 2.

Technical efficacy: Stage 2.